The present invention belongs to the field of molding processes for producing vacuum sealed molds, and in particular, the present invention makes it possible to form the molds which are difficult to mold.
Vacuum sealed molding processes, which have been developed recently as a useful method for making molds, include a step to place a synthetic resin film in tight contact with the surface of the pattern. However, in accordance with the prior art, when the pattern has a deep concave portion or a high convex portion, it is very difficult to stretch the synthetic resin film uniformly over the pattern surface, and therefore the film cannot be applied properly on the bottom or the top surface of the pattern, so that the molds cannot have correct shapes. This presents a great disadvantage.
When performing casting operations using molds by a vacuum sealed molding process, it frequently occurs that the films forming a mold cavity are subjected to the radiation heat of molten metal, and even the film portions not in contact with the molten metal are melted and disappear. If the films are melted in this manner, the charged material loses its original state, which naturally leads to a collapse of the mold. Thus, it is desirable to use a coating material having some shielding effect after the film has melted and disappeared.